Washington Esthetician State Board Practice Exam

Which muscle action is primarily associated with the deltoid muscle?

1. Shoulder flexion

2. Shoulder abduction

3. Shoulder adduction

4. Shoulder rotation

The correct answer is: Shoulder abduction

The deltoid muscle is primarily responsible for shoulder abduction, which is the movement of raising the arm away from the body. This muscle is shaped like an inverted triangle and covers the shoulder joint, with its fibers oriented to facilitate this specific action. The deltoid is divided into three distinct parts: the anterior (front), lateral (middle), and posterior (rear) fibers. The lateral fibers play the most significant role in abducting the arm, especially when the arm is raised to shoulder height. While the deltoid can also contribute to other shoulder movements such as flexion, adduction, and rotation, its primary function and most notable action is indeed abduction. Understanding this function is crucial for recognizing the importance of the deltoid during a wide range of upper body movements and exercises, which rely on the muscle's ability to lift the arm laterally.